The present application generally relates to exhaust aftertreatment systems of internal combustion engine diesel exhaust systems, and more particularly to exhaust aftertreatment systems that include a selective catalytic reduction (SCR) catalyst to control exhaust system emissions. Exhaust aftertreatment systems typically include one or more exhaust treatment catalyst elements, including diesel oxidation catalysts (DOC), diesel particulate filters (DPF), SCR catalysts, and ammonia slip catalysts (ASC).
The aforementioned exhaust treatment catalyst elements can be a source for nitrous oxide (N2O) as a byproduct of NOx reduction and NH3 oxidation processes. Modern exhaust aftertreatment systems are being required to limit emissions based on global warming potential (GWP). Even small quantities of N2O can impact that ability to meet CO2 based fuel economy standards since the GWP conversion of N2O to CO2 is 298 grams of CO2 for every gram of N2O, impacting fuel economy based on CO2 counting. As a result, the ability to implement aftertreatment technologies that provide high fuel efficiencies with high engine-out NOx architectures may be limited due to the increased production of N2O at high engine-out NOx amounts. In addition, catalyst technologies that are highly effective in treating NOx with ammonia as a reductant may be limited due to the production of N2O during NOx reduction. Therefore, a need remains for further improvements in exhaust aftertreatment systems to reduce the emission of N2O into the exhaust environment.